I have had this "thing" for a 14.5 middy. I cant decide what I should do though, should I just buy the barrel and tube and convert my 6920 or should I trade/sell my upper and get a BCM? I dont like mixing and matching on good guns but I cant afford to build/buy a complete upper. I know the difference and the difference wont make a difference at the distances I shoot, but I will build a rifle length one of these days.

The 14.5" has a welded flash suppressor. You have to remove the flash suppressor during installation, so, therefore, the barrel alone is an NFA item.

You can buy a entire tractor trailer full of 14" M4 barrels, perfectly legal. No NFA paperwork needed.

If you decide to use any of the barrels, then a tax stamp would be needed.

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Don't even need a tax stamp if a muzzle device of sufficient length is perma pinned.

Tax stamp only needed if barrel used was still 14" length, on a rifle.

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A AR barrel is never considered the NFA item. (Unless integrally suppressed, but we're not talking cans here) A barrel, when less than 16", and installed on a rifle lower, then makes the rifle subject to NFA rules. Saying that the barrel is the NFA item implys that the barrel itself is subject to regulation which is flat wrong.

When dealing with the alphabet soup crew semantics matter and not knowing exactly what is legal, and worse, perpetuating incorrect interpretations, can get your tit in the wringer real quick.

A AR barrel is never considered the NFA item. (Unless integrally suppressed, but we're not talking cans here) A barrel, when less than 16", and installed on a rifle lower, then makes the rifle subject to NFA rules. Saying that the barrel is the NFA item implys that the barrel itself is subject to regulation which is flat wrong.

When dealing with the alphabet soup crew semantics matter and not knowing exactly what is legal, and worse, perpetuating incorrect interpretations, can get your tit in the wringer real quick.

It all boils down to the same thing once combined. No matter what part it is that makes it a NFA item, together it will get you in trouble.

If you want to try and pick apart others posts make sure yours dont have holes in them. You install a barrel onto the upper reciever not the lower.